The present invention relates to ink jet printers and, more particularly, to the formation of nozzles in a printhead nozzle member for use with an ink jet printer.
Thermal ink jet printers operate by rapidly heating a small volume of ink and causing the ink to vaporize, thereby ejecting a droplet of ink through an orifice to strike a recording medium, such as a sheet of paper. When a number of orifices are arranged in a pattern, the properly sequenced ejection of ink from each orifice causes characters or other images to be printed upon the recording media as the printhead is moved relative to the recording medium.
In these printers, print quality depends upon the physical characteristics of the orifices, or nozzles, in the printhead. For example, the geometry of the nozzles affects the size, shape, trajectory, and speed of the ink drop ejected. Therefore, it is critical that the nozzles formed have the proper taper and that the nozzles are uniform both on the same printhead and from printhead to printhead.
U.S. Pat. No. 5,291,226 to Schantz et al, assigned to the assignee of the present invention, is incorporated herein by reference describes a method for forming tapered ink jet nozzles using a laser ablation technique. A Tape Automated Bonding (TAB) technique is used to form the printheads in long strips of film or tapes which extend between a pair of reels. Sprocket holes are formed in the tape to accurately transport and position the tape beneath a radiation source which is used to form the nozzle members. A metal support layer is positioned adjacent the nozzle member opposite a radiation source such as an excimer laser. The radiation source then provides a selected amount of energy for a selected time period in a selected location to ablate through the nozzle member thereby forming a properly tapered nozzle. A vacuum hole is located in the metal support layer beneath the nozzles is used to remove debris during ablation.
A problem associated with this technique is that the nozzle is not ablated uniformly. As a result a portion of the debris that is to be ablated remains partially attached to the nozzle member and is pulled toward the support member by the vacuum. This partially attached portion of debris referred to as a "trapdoor" remains attached to the nozzle member and is not removed by the ablation process. This debris or trapdoors must be removed in an additional manufacturing step adding to the production cost of the printhead.
In an attempt to prevent trap door formation the vacuum holes beneath the nozzles were eliminated. A problem with eliminating vacuum holes has been damage to the nozzle member in the region proximate the nozzle. Applicants believe that this damage to the nozzle member is due to one of the following mechanisms. The first of these mechanisms is that the support layer reflects some of the energy which is incident on the support layer toward the nozzle member which increases the amount of energy being provided to the nozzle member. This increase in energy provided to the nozzle member results in ablation of additional portions of the nozzle member. Ablation of the nozzle member resulting from reflections from the support layer surface tends to result in poorly defined orifice tapers as well as the ablation of the orifice surface adjacent the support layer or support member. Nozzle members having poorly formed tapers as well as ablated surfaces adjacent the taper form poor quality images on print media.
A second mechanism which can account for the observed damage to the nozzle member is that localized heating of the support layer due to absorption of incident energy from the radiation source which produces conductive heating of the orifice layer. If this conductive heating of the orifice layer is sufficient to heat the orifice layer to a glass transition temperature deformation of the orifice layer adjacent the support layer can occur.
Another problem is that the heating of the support layer surface results in conductive heating of the nozzle member which produces thermal expansions which alters nozzle spacing. Because the heating of the support layer is very localized and for short time durations it is difficult to provide cooling to maintain a support layer temperature that is both uniform sufficiently low to prevent thermal expansion which can alter nozzle spacing or damage to the nozzle member or nozzle member films.
There is an ever present need for techniques for forming tapered nozzles in polymer based nozzle members. These techniques should allow for the reliable formation of properly tapered nozzles with little or no defect. In addition, this technique should allow the nozzle members formed to have a high degree of consistency thereby producing a more uniform and consistent drop size from orifice member to orifice member. Finally, this technique should be well suited to a manufacturing environment to reduce the cost and complexity of the manufacturing process.